Approximately 30% of all colon cancer patients are diagnosed with stage II disease. (Jemal et al., CA Cancer J. Clin., 2004). The 5-year survival for patients with stage II colon cancer treated by surgery is approximately 75-80%, demonstrating that the majority of patients are cured by surgery alone. (Benson, The Oncologist, 2006; Nauta et al., Arch. Surg., 1989.) Nevertheless, approximately 20-25% of these patients will develop recurrent disease within their lifetime. (Benson, The Oncologist, 2006; Gill et al., J. Clin. Oncol., 2004). In theory, these patients should benefit from adjuvant chemotherapy. However, only around 3-4% of patients have an absolute improvement in survival at 5-years with the use of adjuvant chemotherapy in stage II colon cancer. (Benson, The Oncologist, 2006; André et al., Annals of Surgical Oncology 2006). As a consequence, the American Society of Clinical Oncology guidelines recommend that these patients should not be routinely treated with adjuvant chemotherapy. (Benson et al., J. Clin. Oncol., 2004). Despite this, it is clear that approximately 20% of stage II colon cancer patients, at higher risk of relapse, may be candidates for adjuvant treatment. (Benson, The Oncologist, 2006; Nauta et al., Arch. Surg., 1989; Gill et al., J. Clin. Oncol., 2004; André et al., Annals of Surgical Oncology 2006.)
In diseases such as colon cancer, the first treatment is often the most important and offers the greatest chance of success, so there exists a need to use the treatment most effective for a patient's particular stage of colon cancer as the first treatment. This has traditionally been impossible because no method was available for predicting which drug treatment would be the most effective for a particular individual's physiology. Many times patients would needlessly undergo toxic drug therapy. For example, in Stage II tumor node metastasis (TNM) colon cancer, there has been no method of determining which patients will respond to adjuvant chemotherapy after surgery. Only one third of the 20% of stage II patients at risk for relapse after surgery derive any benefit from chemotherapy. This means that prescribing adjuvant chemotherapy exposes some patients to treatment that is unnecessary. Alternatively, a decision to withholding adjuvant chemotherapy at this stage will expose some patients to a higher risk of cancer relapse.
Currently, diagnostic tests used in clinical practice are based on a single analyte test, and therefore do not capture the potential value of knowing relationships between dozens of different markers. Moreover, diagnostic tests are frequently not quantitative, relying on immunohistochemistry. This method often yields different results in different laboratories, in part because the reagents are not standardized, and in part because the interpretations can be subjective and may not be easily quantified. RNA-based tests have not often been used because of the problem of RNA degradation over time and the fact that it is difficult to obtain fresh tissue samples from patients for analysis. Fixed paraffin-embedded tissue is more readily available and methods have been established to detect RNA in fixed tissue. However, these methods typically do not allow for the study of large numbers of genes (DNA or RNA) from small amounts of material. Thus, traditionally fixed tissue has been rarely used other than for immunohistochemical detection of proteins.
Recently, several groups have published studies concerning the classification of various cancer types by microarray gene expression analysis (see, e.g. Golub et al., Science 286:531 537 (1999); Bhattacharjae et al., Proc. Natl. Acad. Sci. USA 98:13790 13795 (2001); Chen-Hsiang et al., Bioinformatics 17 (Suppl. 1):S316 S322 (2001); Ramaswamy et al., Proc. Natl. Acad. Sci. USA 98:15149 15154 (2001), Salazar et al., Journal of Clinical Oncology 29: 17-24 (2010), O'Conneell et al., Journal of Clinical Oncology 28: 3937-3944 (2010) and Kerr et al., Journal of Clinical Oncology 27 (suppl) 15s (2009)). However, these studies mostly focus on improving and refining the already established classification of various types of cancer, and generally do not provide new insights into the relationships of the differentially expressed genes, and do not link the findings to treatment strategies in order to improve the clinical outcome of cancer therapy. In addition, cancer treatment and colon cancer clinical trials are still being pursued on the basis of the availability of new active compounds rather than the integrated approach of pharmacogenomics, which utilizes the genetic makeup of the tumor and the genotype of the patient to establish a personalized medication regime.
Although modern molecular biology and biochemistry have revealed more than 100 genes whose activities influence the behavior of tumor cells, state of their differentiation, and their sensitivity or resistance to certain therapeutic drugs, with a few exceptions, the status of these genes has not been exploited for the purpose of routinely making clinical decisions about drug treatments.